mesa3d: Bump version to 10.2.1, fix xa build

Building xa requires at least one non swrast gallium driver, needed since:
http://cgit.freedesktop.org/mesa/mesa/commit/configure.ac?h=10.2&id=e283e966660fdf037be6353dc96b7f63b8aa315a



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>